Aug 20, 2022
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Climate change in the past has contributed to the rapid evolution of reptiles

Climate change in the past has contributed to the rapid evolution of reptiles

The largest mass extinction in Earth’s history occurred at the end of the Permian period, about 252 million years ago. More than 80 percent of all species that existed at that time have disappeared forever from the fossil record. This changed the nature of life on Earth and ushered in a new era in which reptiles evolved and multiplied. In the past, biologists believed that this rapid expansion of reptiles was due to the abundance of ecological niches vacated by the extinction of Permian species, but a new study suggests that climate change was also an important factor in the spectacular evolution and expansion of reptiles at this time.

“We found that these periods of rapid reptile evolution were closely associated with rising temperatures. Some groups changed very quickly, some less quickly, but almost all reptiles evolved much faster than ever before,” said study lead author Thiago Simoes. (Tiago R Simões), Postdoctoral Fellow, Museum of Comparative Zoology and Department of Organic and Evolutionary Biology, Harvard University.

In the study, Simoes and senior author Prof. Stephanie E. Pierce (also of Harvard), along with colleagues Prof. Michael Caldwell (University of Alberta, Canada) and Dr. Christian Kammerer (North Carolina Museum of Natural Sciences), studied early amniotes. These animals represent the forerunners of all modern mammals, reptiles, birds and their closest extinct relatives at the initial stage of their evolution. At this point in time, the first groups of reptiles and mammalian ancestors split off from each other and developed along their own separate evolutionary paths.

“Reptiles represent an ideal and rare terrestrial system to study this question because they have a relatively good fossil record and have survived a number of climate crises, including those that led to the largest extinction event in the history of complex life, the Permian-Triassic mass extinction,” Simões said. .

In the Permian period, the vertebrate fauna was dominated by synapsids. These were not reptiles, but the ancestors of mammals known as stem mammals or proto-mammals. Most of them died during the Permian extinction, and their ecological niches were occupied by reptiles, including numerous species of dinosaurs that developed and multiplied rapidly during the Triassic period (252-200 million years ago).

The new study, published in the journal Science Advances, uses morphological data from more than 1,000 fossil specimens of 125 species of reptiles, synapsids, and their closest relatives over some 140 million years before and after the Permian-Triassic extinction event. This dataset is 40% larger than the previous largest dataset and most of the measurements were made by direct observations and microtomographic scans.

The researchers analyzed this data to determine when these fossil species first arose and how quickly they evolved using modern analytical methods such as Bayesian evolutionary analysis, which is also used to understand the evolution of viruses such as SARS-COVID 19. They then combined the morphological data with body size information and global temperature data spanning millions of years of the geological record to provide a broad overview of the major adaptive responses of animals to climate change.

The experts found that the emergence of new species, increased rates of morphological change, and changes in geographic distribution corresponded to periods of rapid change in climatic conditions, including global warming and cooling,

“Our results indicate that periods of rapid climate shifts and global warming are associated with exceptionally high rates of anatomical change in most reptile groups as they adapted to new environmental conditions, and this process began long before the Permian-Triassic extinction event, at least 270 million years ago, indicating that the diversification of reptilian body plans was not caused by the PT extinction event, as previously thought, but actually began tens of millions of years before,” said Prof Pierce.

“One lineage of reptiles, the lepidosaurs, from which the first lizards and tuataras descended, went in the opposite direction from most reptile groups and went through a phase of very slow change in general anatomy,” Simoes says. to lose his temper and change radically, like most other reptiles at the time.” The researchers suggest that this is due to the preliminary adaptation of their body size in order to better tolerate high temperatures.

“The physiology of organisms really depends on their body size. Small-bodied reptiles can better exchange heat with their environment. The first lizards and tuatara were much smaller than other groups of reptiles, not so different from their modern relatives, and therefore they were better adapted to extreme changes in temperature. The much larger ancestors of crocodiles, turtles and dinosaurs could not lose heat so easily and were forced to quickly change their bodies to adapt to new environmental conditions.”

According to Prof Pierce, the large-sized reptiles basically took two paths to cope with these climate shifts – they either migrated closer to temperate regions or invaded the water world where they didn’t have to worry about overheating, as the water can absorb heat. and maintain the temperature much better than air.

“Such a close relationship between temperature rise in the geologic past and the biological response of dramatically different groups of reptiles suggests that climate change was a key factor in explaining the origin and explosion of new reptile body plans during the late Permian and Triassic periods,” Simões said.

“We show that the origin and phenotypic radiation of reptiles were not driven solely by ecological opportunities after the end of the Permian extinction event, as previously thought, but were also the result of multiple adaptive responses to climate shifts over a period of 57 million years,” the study authors concluded.

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